Conventional power equipment includes the steam engines, internal combustion engines, and external combustion engines.
Steam engine: It cannot work without the boiler. The whole machine is heavy and large. The pressure and the temperature of the steam cannot be too high, and the exhaust pressure cannot be too low. The heat efficiency is hard to improve. It is a reciprocating machine. The inertia restrains the improvement of the rotational speed. The working is not continuous. The flow of steam is restrained, which limits the improvement of the power.
Internal combustion engine: It has a complicated structure, a high requirement of fuel, and strict requirement of the cleanliness of fuel. It pollutes the environment.
External combustion engine: For example, Stirling engine is one kind of external combustion engine. Compared with internal combustion engine, Stirling engine has the following advantages:
It is suitable for all kinds of energy, not matter what state the energy fuel is, liquid, gas, or solid. When using the heat-carrying system (e.g., heat pipe) to heat indirectly, almost all high-temperature heat source (e.g., solar radioactive isotope and nuclear reaction) can be used, while the engine itself (except the heater) does not need any change. At the same time, Stirling engine does not need a compressing machine to increase the pressure, which can be met by an ordinary fan. The fuel with relatively high impurity content is allowed. The unit capacity of Stirling engine is small, the capacity of which is ranges from 20 to 50 kw. The system capacity can be increased or reduced based on local conditions. The structure is simple. The number of parts of the external combustion engine is 40% less than that of an internal combustion engine. It has a significant margin of price discount and a low maintenance cost.
When Stirling engine is running, the fuel is burning continuously in the combustion chamber which is outside the cylinder. The working medium, which is independent from the gas, absorbs the heat from the heater and works with respect to the outside on the basis of the Stirling cycle. Thus, the knocking and intermittent combustion of the internal combustion engine and the like are avoided. An efficient, less noisy, and low-exhaust operation is realized. As being efficient, the total energy efficiency reaches more than 80%. As being less noisy, the noise at a place which is one meter from the bare machine is lower than 68 dBA. As being low-exhaust, the emission of tail gas meets the standard of Euro 5.
Since the working medium does not burn, the external combustion engine avoids the problem of knocking of the conventional internal combustion engine, such that high efficiency, low-noise, low-polluting, and low-running-cost are realized. The external combustion engine can burn various gasses, natural gas, biogas, petroleum gas, hydrogen, gas, etc. Liquid fuels like diesel, liquefied petroleum gas, etc. can also be used. Burning woods, the solar energy, etc. can also be used. As long as the temperature of the hot chamber reaches 700° C., the equipment will run and work. The lower the environmental temperature, the higher will be the efficiency of the power generation. The most remarkable advantage of the external combustion engine is that the output and efficiency are not affected by the altitude, which makes it very suitable to use in high-altitude areas.
Meanwhile, the mainly existing problems and defects of Stirling engine are as follows. The manufacturing cost is high. The working medium sealing technology is difficult. The reliability and serving life of the sealing part have problems. The material cost is high. The power adjusting control system is complex. The machine is heavy. The costs of the expansion chamber, the compression chamber, the heater, the cooling chamber, the regenerator, etc. are high. The heat loss is twice to three times than that of an internal combustion engine.
Organic Rankine Cycle system includes a pump, an evaporator, an expander, a generator, a condenser, etc. The heat collector absorbs the solar irradiation. The temperature of the heat exchanging medium inside the heat collector increases. The heat is transmitted to the organic working medium from the heat exchanging medium through the evaporator. The organic working medium is heated in the evaporator under a constant pressure. The gaseous organic working medium with a high pressure enters the expander to work through expanding, so as to drive the generator to generate power. The organic working medium discharged from the tail of the expander enters the condenser to condense under a constant pressure. After increasing the pressure by the pump, the organic working medium output from the condenser enters the evaporator, such that one power generation cycle is completed.
Organic Rankine Cycle system has the following defects. The conversion efficiency is low. The size is huge. The expander which has a complex structure is essential to work.
The comparison between the rotor generator and the conventional reciprocating generator is as follows. Both the reciprocating generator and the rotor generator obtain the rotating power from the expanding pressure generated by burning the air fuel of mixed gas. The structural difference between these two types of generator lies in how to use the expanding pressure. In the reciprocating generator, the expanding pressure generated on the surface of the top of the piston pushes the piston downwards. The mechanical force is transmitted to the connecting rod to drive the bent axle to rotate. For the rotor generator the expanding pressure applies on the side of the rotor, to push one of the three surfaces of the triangular rotor to the center of the eccentric shaft. Such a motion is performed under two components of force. One component of force is the centripetal force oriented to the center of the output shaft. The other component of force is the tangential force (Ft) which chives the output shaft to rotate.
Ordinary generator is the reciprocating generator. During working, the piston moves back and forth. In order to convert the linear movement of the piston into a rotation, a slider-crank mechanism is necessary. Different from that, the rotor generator directly convert the expanding pressure of the burning gas into the torque of the rotation. Compared with the reciprocating generator, the useless linear movement is eliminated. Thus, the rotor generator with the same power has a small size, light weight, less vibration, and low noise. It has significant advantages.
The features of the rotor generator are as follows. While the triangular rotor is rotating around a center of the triangular rotor, the center of the triangular rotor rotating around the output shaft at the same time. The inner gear ring whose center is the center of the triangular rotor engaging the gear whose center is a center of the output shall. The gear is fixed to the cylinder and does not rotate. The gear ratio of the inner gear ring and the gear is 3:2. The above motion relation makes a motion trail of a vertex of the triangular rotor (which is a shape of a wall of the cylinder) is in a shape of “8”. The triangular rotor divides the cylinder into three independent sections. The three sections go through air intaking, compressing, working, and exhausting respectively. When the triangular rotor rotates once, the generator ignites and works three times. Due to the above motioned relation, a rotating speed of the output shaft is three times of a rotating speed of the rotor, which is totally different from the reciprocating generator whose motion relation is 1:1 of the piston and the bent shaft.
Advantages of the rotor generator are as follows. The rotor of the rotor engine works three times per rotation. Compared with ordinary four-stroke engine which works once per tow rotations, it has the advantage of a high ratio of horsepower to volume (which means the engine can output more power with a small volume). Moreover, due to the characteristic of axial directional motion of the rotor engine, it can reach a high rotating speed without the precise balance of the bent shaft. In the entire engine, only two transmission parts are included. The structure is significantly simplified, compared with ordinary four-stroke engine which includes more than twenty moving parts including air intake/outtake valve, etc. The likelihood of breaking down is notably reduced. Besides, the advantages of the rotor engine further include small volume, light weight, low gravity center, and less vibration.
Disadvantages are as follows. The fuel consumption is high. The pollution is heavy. Since the compression ratio is not as high as the reciprocating generator, the combustion is not thorough in the rotor generator. Although Mazda Company has added devices like one-stage turbine, one-stage turbine, etc., the output horsepower is increased, and the exhaust gas emission reduced to certain extent. However, it has a remarkable difference from the reciprocating generator. The abrasion is serious, which causes short lifetimes of the parts. Since there is only one radial sealing sheet between adjacent chambers of the triangular rotor engine, the radial sealing sheet always contacts the body of the cylinder linearly. Moreover, the location where the radial sealing sheet always contacts the body of the cylinder is changing all the time. Thus, the three combustion chambers are not completely separated (sealed). The abrasion of the radial sealing sheet is quick. After some time of using the engine is subjected to the problem of gas leaking due to the abrasion of the oil sealing material. The fuel consumption and the pollution is increased sharply. The special mechanical structure results that it is difficult to repair such kind of engines.